The DG-200 provides a physical USB interface to the host computer, but
internally it uses a Prolific PL-2303 chip to do this. So you must have
drivers installed on your computer to recognize the PL-2303 and provide
that data as a serial port to software like GPSBabel. Such software
comes with the unit for Windows. Prolific provides software for Mac OS/X,
but unfortunately their driver has a defect which makes it unstable with
GPSBabel.

erase option

Erase device data after download.

This option erases the track log from the device after download.

erase_only option

Only erase device data, do not download anything.

Much like the erase this optio erases the data in the GPS.
It does not transfer data before doing so, making it much faster. This may
be handy in a work flow where you want to transfer the data from the GPS,
check it on a map, and then remove it from the unit.